1. Field of the invention
This invention relates to portable multimedia computers, and more particularly to a digital audio link to a docking station.
2. Description of the Related Art
Portable computers continue to grow in popularity at a more rapid pace than ordinary desktop personal computers (PC""s). These notebook or laptop PC""s are extremely powerful, having many of the features of state-of-the-art desktop PC""s. Recently, multimedia capabilities have been added to laptop PC""s. Stereo speakers, a microphone, and FM synthesizers and other audio capabilities are built in to many multimedia laptop PC""s.
Docking stations or port replicators have been used to bridge the gap between the capabilities of older laptop PC""s and those of desktop systems. Some docking stations allow expansion or AT-bus cards to be plugged into an industry-standard ISA bus giving the laptop expansion abilities like that of a desktop PC. For example, older laptop PCs did not include audio capabilities. Audio capabilities can be added to these laptops by plugging them into a docking station that had a sound card installed in the ISA bus.
Newer laptop PC""s often contain the equivalent of a sound card. Since sound cards use many of the same fixed resources such as interrupts (IRQ""s), I/O addresses, and DMA channels, it is generally not feasible to have more than one sound card in a PC. Thus, newer multimedia laptops should not be used with a docking station with a sound card unless the laptop""s sound card can be disabled. Unfortunately, disabling the sound-card features in a laptop is not always easy or even possible.
The incompatibility of internal laptop sound cards with docking-station sound cards prevents many docking stations from using sound cards. These docking stations support only analog audio; the digital-sound features of most sound cards are not supported.
The laptop""s sound system generates and outputs analog audio signals, which are sent to the docking station for playing on external speakers connected to the docking station. Audio mixing is not performed by the docking station. Audio from a CD player in the docking station must be mixed with computer-generated sound by a mixer inside the laptop and then output back out to the external speakers.
FIG. 1 shows a laptop PC with a docking station, highlighting audio components. Laptop PC 10 is a multimedia laptop with audio features built-in. A user""s voice can be picked up by internal microphone 14, which is built in to the laptop""s housing. Internal speakers 12 are also built in to the laptop""s housing, and provide stereo sound generated by the internal sound card inside laptop PC 10.
While it is convenient to have a built-in internal microphone 14 and internal speakers 12, the small, compact size of laptop PC 10 prevents the use of high-quality audio components. High-fidelity speakers require a large magnet and large-diameter diaphragm sound cones, which simply do not fit inside a laptop PC.
Laptop PC 10 fits into docking station 20. External connectors are provided on the back of laptop PC 10 to make electrical connection with docking-station connectors 16. Digital signals are included in connectors 16 to control an external expansion bus in docking station 20, such as an ISA bus or a PCI bus (not shown). Other peripherals often included in docking station 20 include connections for a printer, modem, external monitor, or network. Since an audio card in docking station 20 would have resource conflicts with the internal sound card in laptop PC 10, a sound card cannot be added to docking station 20. Instead, analog signals output from the sound card in laptop PC 10 are output to connectors 16. These analog audio signals from laptop PC 10 are routed to high-fidelity external speakers 18 connected to docking station 20. It is difficult or impossible for the user to disable the internal speakers without losing significant quality when using the external speakers in the several prior-art systems.
Analog input from external microphone 22 is sent from docking station 20 to laptop PC 10, as can input from other audio sources connected to a line-in (L/IN) input on docking station 20. Digital or analog-signal mixing of these input sources typically cannot be performed in docking station 20. Docking station 20 may also provide audio amplification since a separate power supply is included in docking station 20.
FIG. 2 highlights connectors on the back of a laptop PC. Parallel-port connector 32 is used to connect to a printer or other parallel device. Serial-port connector 34 is a D-type plug for connecting an external serial device such as an external modem. Connectors 32, 34 are often used without a docking station. A VGA connector (not shown) is also included in many docking stations for connection to an external CRT monitor.
Docking connector 30 is a special-purpose connector containing a variety of signals for connecting to a docking station. While parallel-port connector 32 and serial connector 34 are industry-standard connectors, docking connector 30 is a proprietary connector. Docking connector 30 is only able to fit docking stations made for the specific manufacturer and model of laptop PC.
Docking connector 30 contains address, data, and control signals for an external PCI or ISA bus in the docking station, allowing expansion cards plugged into the docking station""s bus to be controlled by a docked laptop PC. Data from an external DVD or CD-ROM drive in the docking station can also be sent to the laptop PC thorough docking connector 30. Power and ground signals may also be included in docking connector 30. High-speed signals such as digital video data streams are often separated form other signals in docking connector 30 by power or ground signals to act as shielding, preventing cross-talk to adjacent signals.
While analog audio signals from the internal sound card in the laptop PC could be sent through docking connector 30, this is undesirable because of noise injection from high-speed digital signals in docking connector 30. Digital signals operating at high frequencies such as clock signals and video or CD-ROM data streams couple noise into other signals in docking connector 30. Even signals that are not immediately adjacent to the higher-speed signals can suffer from noise injection as common ground signals and the metal housing of the connector can inject noise into all signals in docking connector 30. Thus docking connector 30 is inherently a noisy environment.
Most digital signals have high noise margins, so a moderate amount of noise injection is tolerable. However, analog signals are sensitive to small voltage changes since the voltage level itself conveys the information, such as the sound intensity. Thus, any analog audio signals sent through docking connector 30 suffer from noise injection. The listener notices the noise injection as scratchy or low-quality sounds from any external speakers attached to the docking station.
The severe noise injection of docking connector 30 prevents inclusion analog audio signals in docking connector 30 for higher-quality docking stations. Instead, separate analog audio connectors 36 are provided to connect analog audio signals from a docked laptop PC to the docking station. Audio connectors 36 are often round plugs or jacks with concentric shielding around one or two signal lines, such as standard audio jacks. For example, a speaker connector has two signal lines for the two stereo speakers, surrounded by a ground.
Often three, four, or five audio connectors 36 are used. Stereo outputs from the laptop PC are contained in a speaker connector, while inputs from the docking station to the laptop PC""s sound card are contained in two or three other connectors. These inputs include an external microphone, and external plugs for line-in and line-out signals from a hi-fidelity stereo receiver, tape deck, TV or VCR. Another input audio connector 36 is sometimes included to pass audio from a DVD or CD-ROM drive in the docking station to the laptop PC. Each stereo analog-audio connector has 2 signal lines and one ground, while the mono microphone has one signal and one ground. Thus up to a total of 14 audio signals and grounds can be connected using analog-audio connectors 36.
While such separate analog audio connectors 36 are effective in isolating the sensitive audio signals from the noisy digital signals in docking connector 30, audio connectors 36 are relatively expensive. Additionally, audio connectors 36 are designed for large stereo equipment, not for compact portable computers. The large size of audio connectors 36 requires area on the back panel of the laptop PC.
The size of portable computers is limited. Indeed, a primary reason portable PC""s are purchased is the small, compact size. Area on the back of the laptop PC is at a premium. Often docking connector 30 and other required connectors 32, 34 for the serial and parallel ports occupy most of the available area on the rear of the laptop PC. Thus, there is little area remaining for audio connectors 36. The large, bulky audio connectors do not easily fit on the back panels of many compact laptop PC""s.
FIG. 3 is a diagram of a docked laptop PC with digital and analog connectors to a docking station. PCI controller 44 in laptop PC 10 controls access to internal or external devices on a PCI bus. A graphics subsystem is also accessed by controller 44. PCI controller 44 generates PCI-bus control signals and addresses and transmits these through docking connector 30 to external PCI controller 46. External PCI controller 46 buffers these address and control signals and drives them onto an external PCI expansion bus in docking station 20. Data from expansion cards on the external PCI bus is returned to PCI controller 44 in laptop PC 10 through docking connector 30.
Digital audio controller 40 is accessed by programs executing on a microprocessor in laptop PC 10. Digital audio controller 40 performs equivalent functions to a sound card. Analog-Digital (A/D) converter 42 converts digital audio signals to analog audio signals and outputs these analog audio signals to audio connector 36. A/D converter 42 also receives analog audio inputs from audio connector 36 and converts then to digital audio signals for processing by digital audio controller 40.
Analog audio signals from audio connectors 36 are connected to external analog audio system 50. Amplification of analog audio signals is performed by external analog audio system 50, which drives external speakers and receives audio inputs from an external microphone and perhaps a line-in plug and a CR-ROM drive.
While separate analog audio connectors reduce the problem of noise injection from high-speed digital signals in the docking connector, these audio signals are still routed through a noisy environment in a small form-factor laptop PC. The audio connectors are relatively expensive and consume valuable area on the rear of the laptop PC. It is desired to eliminate these analog audio connectors from a laptop PC to a docking station while still supporting audio functions in the docking station. It is further desired to have a single sound card or system internal to the laptop PC control audio functions both internal to the PC and external in the docking station. It is desirable to have audio mixing of digital audio signals both internally in the laptop and externally in the docking station.
What is desired is a portable PC containing a sound system that can control sound functions including external mixing in a docking station without using a standard sound card in the docking station. It is desirable to have the functions of a sound card in the docking station while also having the audio functions of a sound card inside the laptop PC, without having the conflicts and compatibility problems of having two sound cards in a PC. It is desirable to drive both internal an external speakers and receive audio inputs from both an internal microphone and an external microphone or line input. It is desired to arbitrarily mix these internal and external audio sources. Digital mixing of both internal and external audio sources is desired.
An audio system for a portable personal computer (PC) has an internal audio controller that generates digital audio. An internal analog-digital converter converts digital audio from the internal audio controller to analog audio for playing on an internal speaker.
A docking-station connector connects the portable PC to a docking station. The docking-station connector contains high-speed digital signals for communicating data, address, and control to an expansion bus in the docking station. The expansion bus receives expansion cards to expand functions performed by the portable PC when the portable PC is connected to the docking station through the docking-station connector.
An external digital-audio link uses digital signals in the docking-station connector. It sends the digital audio generated by the internal audio controller to the docking station. Digital-audio signals are sent over the external digital-audio link thorough the docking-station connector. Thus digital audio is generated inside the portable PC and transmitted as digital audio signals to the docking station.
In further aspects of the invention, analog audio signals are not connected from the portable PC to the docking station. Only digital audio signals and not analog audio signals are transmitted to and from the docking station.
In still further aspects a master mixer is coupled to the internal audio controller and to the external digital-audio link. It receives external digital audio from the docking station and mixes the external digital audio with digital audio from the internal audio controller to generate composite digital audio. Thus the composite digital audio is mixed from the external digital audio from the docking station and the digital audio from the internal audio controller.
In further aspects, the internal analog-digital converter is coupled to a built-in microphone and to built-in speakers. The internal analog-digital converter converts analog audio from the built-in microphone to digital audio and converts digital audio to analog audio for playing on the built-in speakers. A music synthesizer generates the digital audio under program control.
The internal audio controller also has an internal mixer that receives digital audio converted by the internal analog-digital converter from the built-in microphone. The internal mixer also receives digital audio from the music synthesizer and digital audio from the master mixer. The internal mixer generates a second composite audio stream from microphone, music synthesizer, and master-mixer audio inputs.
The second composite audio stream is sent to the master mixer for further mixing with external audio sources. Thus audio mixing is performed by the internal audio controller and by the master mixer. The master mixer is further coupled to an internal bus for storing digital audio on a hard disk or a main memory.